The BrewTools MiniUni is a great solution for those that are not interested in one of the more expensive conical fermenter and glycol chiller combination. As I mentioned in my first Blog post about the MiniUni, this is a stainless fermenter that fits inside my refrigerator and comes with a 4" Tri-Clamp ferrule on top and 2" Tri-clamp on the bottom. For me, it ticked all the right boxes, but after my first batch I realised I wanted a better way to dry hop. Read on for my solution!
Take it from the top
Most conical fermenters have one or more Tri-Clamp ferrules at the top which allow connection of various accessories, including a dry hop assembly. The MiniUni uses a single 4" Tri-Clamp ferrule at the top, so if you want to dry hop with a Tri-Clamp dry hopper, you have to figure out how to connect it.
In the shop, we have several fittings that will help, including the 4" to 1.5" NC adapter plate, the 4" reducing tee, and yes you can even mount a 4" butterfly valve and sight glass directly to the top.
Of these options, the 4" x NC/1.5" Tri-clamp adapter is the most economical. You can install a 1.5" butterfly valve and 1.5" sight glass onto that, then cap it with a 1.5" Tri-Clamp NC adapter, but this has some disavantages. For one, you can't easily purge the assembly when it is mounted and filled with hops. Second, the 1.5" diameter opening is prone to blockage from hop pellets. It takes a lot of shaking, opening/closing, and tapping the glass to get everything to fall through. I really don't recommend this method, especially if you need to mount it low profile horizontally or at an angle as shown below. It just does not work well and you will get quickly frustrated.
A better solution would be to install a 1.5" to 2" Tri-Clamp adapter and then a 2" dry hop assembly on top of the 1.5" port. This would allow you to easily purge the chamber, it will be less prone to blockages, and you can fit more hops in it.
The main problem with any of these top mount solutions is that they add quite a bit of height to the top of the tank. For example the 2" Dry hopper with 1.5" reducer adds 38 cm. If you have the space, then this is a great way to dry hop, so go for it! But if you want to put the MiniUni in a fridge for temperature control and cold crashing, you will likely need another solution because there is probably not enough space at the top of the tank inside the refigerator.
Necessity is the mother of invention as they say. I decided to experiment with dry hopping from the bottom of the tank. And why not, I mean, the hops all end up at the bottom anyways! If we could "inject" the hops from the bottom using CO2, this might also provide a way to mix and rouse them during the dry hop period to increase extraction.
First things first. I built a stand out of 30mm aluminum profile. It allows the tank to be installed over the compressor "bump", which is usually at the bottom of the refrigerator. The stand also allows easy access to the bottom of the fermenter to install the necessary parts.
For this process you will want to get part of the dry hop assembly, ideally the sight glass, to be vertical (you will see why later). The "minimum" solution uses the following components:
To acheive this, you can buy the 2" dry hop assembly and add 2 elbows, 2 clamps, and 2 gaskets to complete the set.
If you want to install the butterfly valve directly to the tank instead having an elbow in between, you will need a 5cm spool between the two elbows to allow the sight glass to clear the MiniUni.
It's probably best to try and remove some of that dead yeast and trub from the fermenter before we begin mixing everything up.
The MiniUni does not have the longer 45 or 60 cone shape found on other conical fermenters, so I prefer to install a passive capture chamber at the bottom of the tank that is easy to remove and clean when dumping yeast. When fermentation is starting to slow down, I open the bottom tank valve and let the yeast sludge settle into the dry hop assembly. For better results, rotate the dry hopper so that it is facing down (shown here for demonstration purposes after dry hopping):
If hop sludge comes out the PRV, it may not close properly, if this happens just close the butterfly valve and remove, dump, clean, and sanitize the assembly.
When removing the assembly, close the butterfly valve on the bottom of the tank. Place a container underneath the valve - this is going to get messy! Pull the PRV on the dry hopper to release any pressure in the chamber and disconnect the dry hopper elbow from the butterfly valve. Dump the yeast, clean the assembly, sanitize it, and reconnect it to the tank. Don't forget to clean and sanitize the open end of the butterfly valve before reconnecting.
Hopefully you have just removed a nice thick sludge of dead yeast and trub from the tank. It's probably better not to mix all that gunk up with the hops during the mixing process to follow.
FYI, the 2" elbow and sight glass hold about 500mL.
Now it's finally time to dry hop!
Preparation is the key to success
Roll and squeeze you hops package to break up any clumps before pouring them in the dry hopper. With the sanitized assembly installed on the tank again, remove the 2" NC adapter from the top of the sight glass and pour in your hops. Clean any hop powder from the Tri-Clamp flange on top of the glass and reinstall the 2" cap on top of the sight glass.
Warning! If you use too much hops or the hop pellets are small, you may end up creating a "hop cement" that blocks the 2" fittings. If this happens, the job will get way more difficult or even impossible.
My recommendatiion is to use less than 150g of hops per dry hopping. If you want to add more hops than that, do a second dry hopping.
Now you will want to purge as much oxygen out the dry hopper as possible. Connect your CO2 to the NC valve on the assembly and fill the chamber with CO2. I usually set my regulator to around 1-1.5 bar. To purge oxygen, pull the PRV on the dry hopper to release the air/CO2 mixture. Repeat this 5-6 times.
Make sure you have a one-way check valve on your CO2 line to prevent backflow of sludge into your regulator.
A more advanced method of purging is to loosen the tri-clamp between the butterfly valve and the 90 elbow of the dry hopper, but not more than 2 complete turns. Hold the clamp in place with your hand to help prevent accidental release. This should create a leak in the dry hopper which, when the CO2 is turned on, will push more oxgen out directly through the hop pellets. Theoretically the clamp could come open and the assembly fall off, so if you do this, do so at your own risk, and be very careful!
Stir it up
To get the system moving and enhance the mixing and hop rousing process, we will use a combination of CO2 pressurization and depressurization of the dry hopper to get the hops at the bottom of the system to move back and forth between the MiniUni and the dry hop assembly. This mixing process is straightforward:
- Depressurize the MiniUni and the dry hopper.
- Open the butterfly valve at the bottom of the tank.
- Turn on the CO2 at the dry hopper.
- Turn off the CO2 after 4-5 seconds.
- Very slowly and carefully pull the PRV on the dry hopper. Hopefully, beer and or hops will move out of the tank, up the glass towards the PRV.
- Close the PRV before the beer / hop sludge comes into contact with it! That can prevent the PRV from sealing, and you will have to remove the PRV and clean it with a brush to get it to seat again.
- Go back to step 3 and repeat the process until you are satisfied with the mixing.
With any luck, beer will flow up into the hop pellets and the hops will move through into the fermenter. However this is not always the case, you may not see anything happen at first. Do not despair! Here are some tricks to help the process along:
- Increase the pressure in the system. At around 2.5 bar the red PRV on the dry hopper will start to open up, so I would keep it around maximum 2 bar.
- Opening and closing the butterfly valve can help break up any blockage.
- Relieve pressure from the top of the MiniUni after running a number of pressurize / depressurize cycles. This will maximize the pressure differential.
- Let the hop pellet/beer mixture rest for a while to further dissolve the hops before trying again.
If your reaction time is too slow, and you find your PRV is clogging too frequently, you can add an extension tube between the sight glass and the end cap. This will give you a bit more time to close the PRV before the sludge comes out the top.
I like to rouse the hops to increase hop extraction by repeating the mixing procedure a few times over the dry hop period. In between, residual CO2 will begin to carbonate your beer, if you don't want that to happen make sure to depressurize the tank from the top after mixing is completed.
Here is a video demonstrating the setup, preparation, and dry hopping process: